1. Technical Field
This invention relates generally to circuit board testing, and more particularly to a new and improved apparatus for interfacing a circuit board to existing circuit board testing equipment.
2. Background Information
Circuit board testing includes the testing of printed circuit boards (PCB's), backplanes, wirewrap boards, and circuits with conventional and surface mounted devices (SMD's) or a large number of sockets. It often proceeds with the aid of a testing system or host machine designed to supply test signals to the circuit board and detect resulting circuit board signals. Doing this under computer control enables thorough analysis of the circuit board during development and efficient testing during production.
A conventional computerized host machine, for example, generates various host signals, such as supply voltages, input signals, and control signals, for use in causing the circuit board to function throughout a predetermined range of operating conditions. As this is done, a detection portion of the host machine senses resulting circuit board signals for analysis. In this manner, complex testing proceeds with significant speed and flexibility and little operator involvement.
However, connecting or interfacing the host machine signal lines to the circuit board presents certain problems that need to be overcome. First, the circuit board may have a large number of miniature components of varying sizes, and each component lead may constitute one test point to which to connect the signal lines. In addition, the circuit board may be double-sided with test points on each side, so that in many cases the circuit board may have well over a thousand test points with spacing between adjacent test points on the order of one millimeter.
Furthermore, the pattern in which the test points are disposed on one type of circuit board is usually unlike the test point pattern of another board. This further compounds the problem of connecting the host machine signal lines when use with more than one type of circuit board is contemplated. Thus, the task of interfacing the host machine involves numerous connections so that the interfacing equipment is of recognized significance, and each detail of design correspondingly important.
Existing equipment for interfacing a circuit board to a given host machine often takes the form of a fixture dedicated to use with a particular host machine and a specified circuit board. The fixture serves as a support structure with which to hold the circuit board, and it includes a host machine interface, such as a cable connector or a contact panel, for connecting the host machine signal lines electrically to an array of commercially available spring contact probes mounted on the fixture.
The host machine interface is configured to mate with an output connector arrangement on the particular host machine employed, and the probes are arranged in a probe pattern adapted to mate with the test point pattern on one side of the specific circuit board to be tested. Thus, the fixture holds the circuit board and retains the probes in contact with the test points, thereby interfacing the circuit board to the host machine for testing purposes.
Although providing an interface, such dedicated equipment suffers from the drawback of being relatively expensive. It involves the fabrication of a different fixture for each different host system and circuit board to be tested, or at least rather complex modifications to accommodate them. Consequently, it is desirable to have a new and improved interfacing apparatus that overcomes this concern to enable use with various host machines and circuit boards.
Apart from the dedicated nature of existing interfacing equipment, certain other drawbacks need to be overcome. For example, some existing equipment employs a moving plate that accepts and retains the circuit board under vacuum pressure. The vacuum pressure holds the circuit board in a position against the plate such that the probes contact the test points, and this is done to test one circuit board side at a time.
This results in a test procedure that is somewhat inconvenient and time consuming. In addition, the use of vacuum pressure requires a more complex fixture that fits the contour of the specific circuit board to be tested, not just mate with the test point pattern. Although pneumatically actuated techniques have been employed in some fixtures, these also limit testing to one side at a time. Consequently it is desirable to have a new and improved apparatus that overcomes this concern also, to enable convenient testing of fully loaded, double-sided circuit boards.
Furthermore, existing interfacing equipment often employs a pair of platens which close like a clam shell upon the circuit board in order to move the probes into contact with the test points. However, the clam shell action causes the probes to move slightly in a direction parallel to the circuit board surface so that the probe tips slide across the test points during loading, often abrasively. This frequently causes damage to the circuit board components, as well as the probes, so that an improved loading action is desirable as well.
Moreover, existing interfacing equipment often impairs operator diagnosis of the circuit board or test equipment. It does so because the operator cannot conveniently connect the test probe of an oscilloscope or other instrument to the test points when the circuit board is mounted within the fixture. Instead, the operator must open the fixture to gain access to the circuit board test points, and this involves additional time and inconvenience. Therefore, it is desirable to have an interfacing apparatus that overcomes this concern with features enabling such operator diagnostics without disconnecting the circuit board.